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End of session

High level disinfection

e.g. Before ERCP

Before use in



After patients with

pulmonary tuberculosis 20 5* 5*

After a patient with known

infection with M. avium

intracellulare on other

highly resistant

mycobacterium 60-120 5* 5*

* Sporicidal activity is achieved in 10 minutes.

(ii) Peracetic acid Peracetic acid was introduced in 1955 as a disinfecting agent

or sterilant, and is mainly used in the food and the sewage treatment industry. It

has been used for decontamination of plastic isolators and medical equipment,

but rarely in the UK. Its constituents are hydrogen peroxide and acetic acid and,

as a concentrate, it is corrosive and irritant. It acts by releasing free oxygen and

hydroxyl radicals and decomposes to oxygen, water and acetic acid.

Peracetic acid has rapid activity against vegetative bacteria, fungi, bacterial

spores and viruses (28- 31). Vegetative bacteria, including mycobacteria, are

killed in under 5 minutes and Bacillus subtilis spores are destroyed in less than

10 minutes. There are two commercially available preparations : 0.2% peracetic

acid ('Steris') has been shown to reduce M.tuberculosis and M.avium

intracellulare by 5 logio in 15 minutes (17) and 0.35% peracetic acid (Nu Cidex)

has shown reductions in M.tuberculosis H37Rv, M.avium intracellulare,

M.kansasii, and M.chelonae in 4-5 minutes (32). Peracetic acid has been shown

also to be active against a range of viruses, including poliovirus, rotavirus (33),

HBV, and HIV (34). Manufacturer's tests using a 0.35% solution have shown log

reductions of over 8 in suspension and surface tests with herpes simplex and

poliovirus in less than 5 minutes immersion. Prevention of excystation of

cryptosporidium has been reported with 0.2% and 0.35% solutions (35).

Unlike 'Nu Cidex', the 'Steris' peracetic acid can be used only in a dedicated

machine (Steris System Processor) (36). This utilises 0.2% peracetic acid at an

elevated temperature of 50°C in an enclosed machine. The disinfectant exposure

time is 12 minutes with an overall process time of approximately 30 minutes. The

machine is not marketed as a washer/disinfector but as a steriliser as it uses a

sporicidal agent, once only, and rinses processed items in sterile (bacteria free)

water. The disinfectant, 35% peracetic acid, is supplied in a twin compartment,

single dose, carton. This is punctured automatically when it is placed in the

machine. As filtered water enters it dissolves the constituents and produces a

working strength of 0.2% peracetic acid. The unit would appear to be user-safe

and highly effective in disinfecting/sterilising flexible and heat sensitive rigid

endoscopes but it is expensive, takes only one flexible endoscope at a time and

the long-term effects on some endoscope components are yet to be established.

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